As far as league play in North America goes ESEA is still by and large the best to play in, especially with league fees being eliminated from Open. UGC still exists but has been getting smaller over the past few years, and a competitor called TFCL has emerged but it's not very popular outside of Ultiduo cups (though I believe they're hosting a LAN in november?). TF2PL is the newest and best place to find a quick and relatively quality pug, though PugChamp is akin to older PUG sites with better server/UI implementation. For lobbies, TF2Center still exists but it's a pretty piss poor service for a number of reasons you can find just by searching the words "TF2C" and "bad" and looking through the first threads that pop up. TF2Stadium launched as an open source, better implemented alternative, but it experienced a lack of a playerbase and as far as I can tell you can't even log into the site anymore.
TLDR: ESEA is still best p2p, UGC and TF2CL are the 2 competing f2p leagues, and TF2PL is the place to pug
edit: TF2PL's requirements for direct placement (and their goal skill levels probably) are sub-mid open for Beginner, mid-open to low-IM for Amateur, Mid IM-Invite for Advanced, and an all-invite queue (or prem in the EU queues) for Invite